(Not applicable)
This invention relates to planer oxide fuel-cell stacks.
In a planar solid oxide fuel cell (SOFC) stack, individual planar cells comprising a tri-layer structure of anode, electrolyte and cathode, are series-connected to a bipolar plate, also referred to as an interconnect. The interconnect must be impervious with no connected porosity to ensure that fuel and air do not mix. At the same time, the interconnect must be an excellent electronic conductor. While considerable work has been reported on ceramic interconnects, it is increasingly believed by many that cost-performance targets will likely be met only if one uses metallic interconnects.
In the design of any planar stack, channels or grooves must be provided in order to allow the transport of gaseous fuel and air across respective anode and cathode surfaces of the cell, with a minimum of resistance to their flow. Usually, this is accomplished by introducing channels or grooves in the interconnect with the cell being smooth or flat, although designs have been proposed wherein grooves or channels are incorporated in the structure of the cell itself, with the interconnect being smooth and flat. In the former design, the required machining considerably increases the cost. In the latter design, the interconnect is merely a thin sheet of an appropriate metallic alloy. However, considerable processing and cost may is associated with the shaping and fabrication of cells with the required grooves or channels.
Clearly, the desired preference is to have both the cells and interconnect flat, from the standpoint of cost. But, at the same time, channels or grooves are required for the transport of gaseous fuel and air. This can be accomplished by configuring interconnect out of physically separate components, all of which are inexpensive.
The present invention is an interconnect that is inexpensive and simple to manufacture, which will materially simplify and lower the cost of SOFC stacks. The interconnect comprises two border pieces, a first and second border piece. Each border piece is of metal and is generally flat. Each is shaped with an internal cutout shaped such that there is an internal cavity with wide margins on opposing sides of the cavity. Within each margin are holes. In the first border piece, the holes are for the passage of reducing gas. In the second border piece the are for the passage of oxidizing gas.
Between the border pieces is disposed an interconnect foil of an electrically conducting material. On its border region are holes for passing reducing gas passage and holes for passing an oxidizing gas passage. The reducing gas passage holes of the interconnect foil are in registration with the reducing gas passage holes of the first border piece and the oxidizing gas passage holes of the interconnect foil are in registration with the oxidizing gas passage holes of the second border piece. Accordingly, the reducing gas passage holes of the interconnect foil allow passage of reducing gas into and out of the cavity of the second border piece, and the oxidizing gas passage holes of the interconnect foil allow passage of oxidizing gas into and out of the cavity of the first border piece.
Disposed in each of the cavities of the first and second border pieces, are wire gauzes, a first and a second metallic wire gauze. When the interconnect is placed in a connecting and sealing position or relationship between two series connected cells in a stack, the first wire gauze provides electrical continuity between an anode cell surface and the surface of the interconnect foil. The second wire gauze likewise provides electrical continuity between an cathode cell surface and the surface of the interconnect foil.